Evaluation of Thermal Stability of 1/2-Scale Demonstration System of Skeleton Cyclotron for Cancer Therapy

We are developing “skeleton cyclotron”, an ultra-compact high-intensity accelerator for stable generation of radio isotope (²¹¹At) for targeted α-particle therapy, which is expected to be effective in treating refractory cancer (multiple metastatic cancer). The coil system of the skeleton cyclotron consists of three types of air-core no-insulation (NI) REBCO coils: circular main and center coils and non-circular sector coils. The main and center coils generate isochronous magnetic fields to maintain a constant particle rotation period. The sector coils generate azimuthally varying magnetic field to prevent divergence perpendicular to the beam acceleration plane. We designed and fabricated a 1/2-scale demonstration model of the NI-REBCO coil system for the ultra-baby-skeleton-cyclotron (UBSC) coil system, and conducted experiments to investigate its electromagnetic, thermal, and mechanical properties. In this study, the electromagnetic interaction between coils and the process leading to thermal runaway were evaluated numerically for the NI-REBCO coil system for UBSC when a local degradation occurs in one of the coils that compose the NI-REBCO coil system. For numerical simulation, we used the hybrid method of current distribution analysis based on a partial element equivalent circuit (PEEC) model and thermal analysis based on the 2D finite element method.